There are three main methods of building underwater tunnels: tunneling shields, tunnel boring machines, or immersed tubes. Tunneling shields and tunnel boring machines dig deep into the earth or the ocean floor and create the tunnel walls as they go. Immersed tubes are constructed on the ground, sealed, floated, and then placed in a trench that has been dredged and covered with material .
The first step of constructing underwater tunnels is to create a plan. This involves surveying the area to determine the best route for the tunnel, which will involve taking into consideration the existing terrain, soil type, and other environmental factors.
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